1. Field of the Invention
This invention relates to ripple carry adders and particularly to such an adder realized through optoelectronic logic using only AND and OR gates.
2. Discussion of Related Art
There is a fundamental difference between optical circuits, in which the information carriers are photons, and electronic circuits, where the carriers are electrons. In the former case the carriers do not interact with each other, while in the latter they do. This means that in optical devices there exist interconnect possibilities that do not exist with electronic hardware, in particular, interconnected parallel architectures which permit digital arithmetic and logic operations to be performed in a completely parallel, single step process. After the inputs are switched on, the output appears in the time it takes a photon to transit the device. No faster computation time is possible.
Optoelectronic logic circuits have been suggested in the past. For example, MacDonald et al. U.S. Pat. No. 4,506,151 discloses logic circuits which employ photoresponsive field effect transistors to directly drive laser diodes to provide optical output signals in response to optical input signals. However, such known optoelectronic circuits suffer from the defect that electronic inverters are used. The use of inverters limits the depth of logic that can be obtained before a conversion back to optics is necessary.